The present invention relates to a covering material composition for a golf ball, which has excellent resilience, durability and appearance and which also realizes a soft feeling, equivalent to that of a wound golf ball, when the ball is struck and a process for producing the composition.
Ordinary golf balls are classified into wound golf balls and two-piece golf balls. The two-piece golf balls are composed of a core made from a rubber composition and a cover material made from, for example, an ionomer resin (an ionic ethylene copolymer resin), excellent in the impact resistance and resilience, covering the core. Since the two-piece golf balls have a long carry and excellent durability, they are used by many golfers. However, as for the feeling realized by striking the golf balls, many golfers are fond of a soft feeling realized by striking the wound golf balls; the feeling realized by the two-piece balls is hard. Recently the development of a two-piece golf ball which realizes a soft feeling like that of the wound golf balls has been demanded.
In order to obtain the soft feeling upon the striking by softening the two-piece golf ball, a soft ionomer resin mixture of an ionomer resin having a high hardness and another ionomer resin having a low hardness is used as the covering material for the golf ball (Japanese Patent Laid-Open Nos. 308577/1989 and 3931/1993); or a rubber or elastomer selected from among various kinds of them is blended in the covering material (Japanese Patent Laid-Open Nos. 79017/1994, 359025/1992, 78855/1986, 36347/1986 and 133440/1980, and U.S. Pat. No. 3,454,676). However, since the impact resilience of the ionomer resins is reduced as the hardness of them is reduced, the soft ionomer resin mixture obtained by mixing the ionomer resin of a high hardness with the ionomer resin of a low hardness and a low impact resilience has a reduced resilience. Another problem caused by the blending of the materials different from each other is that the durability and the appearance of the buffed golf ball are damaged by the blending.